(57) The present invention provides a method for growing single crystals of a dissociative compound by pulling with a volatile component gas of said dissociative compound sealed at a controlled pressure in a heated growth chamber in which the single crystals are pulled, wherein a partition pipe having a smaller density than the density of melt of the dissociative compound is disposed so as to immerse its lower end in the melt and the melt is covered with B₂O₃ at either one of the inside or outside of said partition pipe. The method of the present invention enables the precise, appropriate control of the melt composition during the course of growing and thereby provides single crystals free from any detrimental contamination and undesirable dislocation problems. The thus obtained crystals are especially desirable for use as substrates for high speed and/or optical devices, because of their excellent semi-insulating properties.